The Oklo Reactor: The World’s Only Natural Nuclear Reactor

Nuclear power is often perceived as a technology that defies the natural order – but simply head to Africa and you’ll find the world’s first and only natural nuclear reactor. Located in the Oklo region of Gabon in Africa, the Oklo Reactor consists of 16 uranium-rich sites where self-sustaining nuclear chain reactions took place billions of years ago. The reactors ran for a few hundred thousand years, averaging 100 kW of power output during that time.

As Atlas Obscura reports: “Two billion years ago, the uranium-rich mineral deposits became flooded with groundwater, setting off a self-sustaining nuclear chain reaction. The energy that was subsequently released then raised temperatures enough to begin boiling away the water, but when the mineral deposits eventually cooled down the nuclear reactions would start back up again… this start-stop fashion at intervals of about two and a half hours.” While “in operation,” the reactors were able to generate approximately 100 kW of power.

The existence of the reactor was first discovered back in 1972 by French physicist Francis Perrin. What started as a routine spectrometry check by the Pierrelatte uranium enrichment facility in France, revealed a discrepancy in the amount of the U235 isotope in the area. Scientists took to investigating the difference to account for all fissionable isotopes — they needed confirmation that none were being diverted to build nuclear weapons.

After a series of measurements were undertaken comparing the site with other large deposits nearby, it was discovered that the uranium ore at this particular location had U235 concentration that was significantly lower. Subsequent examination of other isotopes showed similar anomalies, such as with the levels of Nd and Ru. However, it was this loss in 235U that signaled they had a nuclear reactor in their presence. Since then, 15 other natural nuclear fission reactors were discovered in the Oklo region.